Sometimes I get the following error while I was doing HttpWebRequest to a WebService. I copied my code below too.
System.Net.WebException: Unable to connect
For me, I wanted to start the mongo in shell (irrelevant of the exact context of the question, but having the same error message before even starting the mongo in shell)
The process 'MongoDB Service' wasn't running in Services
Start cmd as Administrator and type,
net start MongoDB
Just to see MongoDB is up and running just type mongo, in cmd it will give Mongo version details and Mongo Connection URL